USB Vocabulary

HCD - Host Controller Driver

UDC - USB Device Controller

USB OTG

All Allwinner A-series SoCs come with one USB OTG controller.
The controller has been identified as a Mentor Graphics Inventra HDRC
(High-speed Dual Role Controller), which is supported by the "musb" driver.
However, the register addresses are scrambled.

The USB OTG controller is connected to a port controller.
Only the data pins are exported from the SoC.
The port controller is also used to control or tune the USB PHYs
for the other USB host controllers.